1. Field of the Invention
The present invention relates to a high-frequency dielectric ceramic composition, and to a dielectric resonator, a dielectric filter, a dielectric duplexer, and a communication apparatus using the same.
2. Description of the Related Art
Dielectric ceramic components are widely used as dielectric resonators and dielectric filters which are mounted in electronic devices, such as portable phones, personal radio equipment and satellite broadcasting receivers, used in high-frequency bands including microwave bands and millimeter-wave bands. These high-frequency dielectric ceramic components require high dielectric constants and high Q values, and adjusting of the temperature coefficient of the resonant frequency to appropriate values near zero.
Examples of disclosed dielectric ceramic compositions include a BaO--Nd.sub.2 O.sub.3 --TiO.sub.2 --PbO composition (disclosed in Japanese Examined Patent Publication No. 56-26321), a BaO--Nd.sub.2 O.sub.3 --TiO.sub.2 --Bi.sub.2 O.sub.3 composition (disclosed in Japanese Examined Patent Publication No. 59-51091), a BaO--Nd.sub.2 O.sub.3 --Ce.sub.2 O.sub.4 --Sm.sub.2 O.sub.3 --TiO.sub.2 --Bi.sub.2 O.sub.3 --Fe.sub.2 O.sub.3 composition (disclosed in Japanese Laid-open No. 63-237304), and a BaO--Nd.sub.2 O.sub.3 --Sm.sub.2 O.sub.3 --TiO.sub.2 --Bi.sub.2 O.sub.3 composition (disclosed in Japanese Laid-open No. 4-104946).
These conventional BaO--Nd.sub.2 O.sub.3 --TiO.sub.2 --PbO and BaO--Nd.sub.2 O.sub.3 --TiO.sub.2 --Bi.sub.2 O.sub.3 compositions have low Q values with respect to relative dielectric constants .di-elect cons..sub.r, which are of insufficient levels for dielectric resonators. In the BaO--Nd.sub.2 O.sub.3 --Ce.sub.2 O.sub.4 --Sm.sub.2 O.sub.3 --TiO.sub.2 --Bi.sub.2 O.sub.3 --Fe.sub.2 O.sub.3 composition, the Q value is improved but relative dielectric constant is decreased to an insufficient level in practical use by the addition of Fe.sub.2 O.sub.3. Although the BaO--Nd.sub.2 O.sub.3 --Sm.sub.2 O.sub.3 --TiO.sub.2 --Bi.sub.2 O.sub.3 composition has a high Q value, the Q value is unstable due to oxygen defects which are formed by reduction during the sintering process.